The invention relates to an energy storage device for an AC voltage grid.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
An energy storage device of the aforementioned type is for example known from US 2014/034873 A1. The energy storage device described therein can have multiple batteries, which can individually or together be connected with a connector to connect the energy storage device with an AC voltage grid. When the battery is discharged it is connected in parallel with a charged reserve battery by a Hot-Swap-Controller and then the discharged battery is disconnected. This enables a continuous energy flow from the energy storage device into the AC voltage grid.
A disadvantage of such a connection is that compensation currents can flow between the batteries because the charged battery always generates a greater direct voltage than the discharged battery. In order to prevent such a compensation current when connecting two batteries in parallel to each other each individual battery is connected to the remaining part of the energy storage device via a direct voltage converter or DC-DC-converter. This renders the production of the energy storage device component- and cost-intensive.
It would therefore be desirable and advantageous to provide an energy storage device for a stationary AC voltage grid for storing energy.